Research from the University of Otago compared birth outcomes in woman using self-employed midwives and those using a doctor, and reported the former group are risking the health of their baby.

But Auckland University's head of obstetrics and gynaecology Lesley McCowan says our midwives provide a high quality of care.

"The risk of babies dying during labour has become significantly reduced. That's a reflection of high-quality care."

She says the way in which the data was gathered means the findings are limited.

"What the study doesn't tell us is how many women are transferred, or receive a consultation with a specialist, and we think approximately 30 percent of women would get a referral at some stage in their pregnancy."

College of Midwives chief executive Karen Guilliland said midwives were under pressure, and the research highlighted a need for improved funding and better staffing of maternity services.

"The differences in that outcome may be explained by the way our maternity services have to operate. Most of our maternity hospitals are understaffed and often struggle to provide immediate response when midwives request medical input.

"This means that often women in labour have to wait to see a specialist, causing unacceptable delays for them and their babies. None of our main maternity hospitals have an obstetric consultant on site after hours or weekends, which are when the majority of births occur."

The Ministry of Health has referred the study to the National Maternity Monitoring Group for advice on whether further research needs to be undertaken.